During initial system startup, the boot loader(8) reads device.hints(5). This file stores kernel boot information known as variables, sometimes referred to as “device hints”. These “device hints” are used by device drivers for device configuration.
Device hints may also be specified at the Stage 3 boot
loader prompt, as demonstrated in 節 12.2.3, “階段三”.
Variables can be added using set
, removed
with unset
, and viewed
show
. Variables set in
/boot/device.hints
can also be overridden.
Device hints entered at the boot loader are not permanent and
will not be applied on the next reboot.
Once the system is booted, kenv(1) can be used to dump all of the variables.
The syntax for /boot/device.hints
is one variable per line, using the hash
“#” as comment markers. Lines are constructed as
follows:
hint.driver.unit.keyword="value
"
The syntax for the Stage 3 boot loader is:
set hint.driver.unit.keyword=value
where driver
is the device driver name,
unit
is the device driver unit number, and
keyword
is the hint keyword. The keyword may
consist of the following options:
at
: specifies the bus which the
device is attached to.
port
: specifies the start address of
the I/O to be used.
irq
: specifies the interrupt request
number to be used.
drq
: specifies the DMA channel
number.
maddr
: specifies the physical memory
address occupied by the device.
flags
: sets various flag bits for the
device.
disabled
: if set to
1
the device is disabled.
Since device drivers may accept or require more hints not listed here, viewing a driver's manual page is recommended. For more information, refer to device.hints(5), kenv(1), loader.conf(5), and loader(8).
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